1. Field of the Invention
The present invention relates to a method for using signals scattered by one or more targets for determining position and velocity of each target. The invention is especially useful in the case where the positions in space and velocity vectors for a very large number of targets are to be determined. The invention is for instance intended for use with the system for determining position and velocity of targets for which this day a patent has been applied with Hans Hellsten as inventor, and which patent application 0101661-7 is hereby incorporated by reference when regarding a more detailed reasoning of the system of transmitter and receiver, henceforth called stations.
2. Description of the Related Art
The invention is based on a 3-dimensional position space and a 3-dimensional velocity space, which together form a 6-dimensional state space with up to ˜1020 cells, where in principle each cell shall be assigned the value 0 (no target) or 1 (target). The large number of cells in the state space place special requirements on the signal-processing method, and one possible method is dealt with in said patent application by Hellsten. In the present patent application an alternative method is suggested.
Due to the large number, ˜1020, of cells in the state space, known projection methods are slow and cumbersome. The simplest known method is where all conceivable target positions are formed for three stations and N targets. They will be fewer than N3 in number, and it is easy to determine position as well as velocity vector for the target for every possible target position. In this way ˜N3 candidates are obtained, each of which Is then supported or discarded by further independent measurements. This gives a method of processing which requires K N3 operations. If K Is large then this method can be much too slow for Interesting values of N.
A specific property of the systems for which the use of the present method is intended is, according to the above, that the information in an introductory, detecting phase can be regarded as binary, which can be utilised. Further the input is from the beginning distributed between different stations. This means that a local, distributed processing which calculates parameters of position and velocity for the targets gives an advantage, as one then receives a paralleling effect on the sensor-near level. A comprehensive communication between stations is then necessary.
The stumbling block is the association problem, which is to in a correct way pair together data from different radar stations. An association where it is unclear whether it is correct or not can be called a candidate. Gradually it becomes clear whether a candidate is a correct association, that is a target, or a false association, sometimes called a ghost. The problem is then to handle the initially very large number of ghosts, that is to find the targets among all candidates.